These ancient tombs may have been more than just a final resting place.
According to researchers from the UK’s Nottingham Trent University (NTU) and the University of Wales Trinity Saint David, Portugal’s 6,000-year-old passage graves located in Carregal do Sal could have also served as the first lens-less astronomy telescope for prehistoric humans.
"The key thing is that a passage grave with its long corridor acts like a telescope that does not have a lens – it is a long tube from which you are looking at the sky," co-author and astronomer Fabio Silva from the University of Wales Trinity Saint David told The Guardian. "Its characteristics are going to impact how you are looking at the sky in three or four ways."
The passage directs your attention to a particular portion of the sky, while also blocking out the distraction of other stars and planets, creating a tunneling effect. Since the structure was likely pitch-black, it would help your eyes adjust to the dark, making it easier to spot fainter details like distant stars.
The team thinks that 13 of the passage graves in Portugal contain entrances that are positioned for a specific purpose: to align with the star Aldebaran.
"The orientations of the tombs may be in alignment with Aldebaran, the brightest star in the constellation of Taurus," Silva said in an NTU press release. "To accurately time the first appearance of this star in the season, it is vital to be able to detect stars during twilight."
The researchers suggest that prehistoric humans might have used the tombs as a calendar aid, helping them mark the changes in seasons, and that they were also possibly used as a ritualistic structure.
Silva and the team are currently testing their hypotheses by simulating the conditions of the passage graves in the lab. "We are going to simulate this star rising at twilight conditions and allow people to tell us when they can see it," Silva told The Guardian. "Then [we will] compare that with a control group of people that are in a room which would replicate the conditions of being outside the passage grave."
Interestingly, a large number of Europe’s passage graves share another unexplained happenstance.
"There are more than a thousand passage graves along the Atlantic coastlands of northwest Europe," archaeologist Timothy Darvill from Bournemouth University in the UK, who was not involved with the study, told the The Telegraph.
"Some, including the well-known examples at Newgrange in Ireland and Bryn-celli-Ddu on Anglesey, seem to have been orientated towards either the sunrise or sunset on the summer or winter solstice," Darvill continued. "But only about 10 percent of passage graves seem to have these orientations. It would be wonderful if the proposed research could identify patterns that apply to the other 90 percent."
The researchers presented their study at the National Astronomy Meeting in Nottingham this week. Their paper has yet to be published.